Hammer Head Research Articles

Centre of mass kinematics of the hammer and thrower during different hammer-throwing drills utilised for training

ABSTRACT During elite-level hammer throws, the vertical displacement of the centre of mass (COM) of the thrower and hammer are approximately 180° out of phase (the hammer’s COM is at its high point when the thrower’s COM is at its low point, and vice versa) prior to the hammer’s release. This out-of-phase coordination pattern contributes to the velocity of the hammer, which ultimately contributes to the distance thrown. Several drills are used to improve coordination between the thrower’s and hammer’s COM, but it is not currently known if the out-of-phase pattern is present during these drills. This study examined the relative phase between the COM of the hammer and thrower during two different rotational drills: The Double Hammer Head and Single Arm drills. Using a 12-camera motion analysis system, COM kinematics for both the hammer and thrower were examined for seven NCAA Division I throwers during the two drills. Contrary to their purported purpose, the phase angles between thrower’s and hammer’s COM were significantly different from 180° during both drills. Further research should be conducted to examine the mechanical factors of hammer throwing drills, as well as the effect such drills have when implemented within training programs.

Inverse lithography technology: 30 years from concept to practical, full-chip reality

In lithography, optical proximity and process bias/effects need to be corrected to achieve the best wafer print. Efforts to correct for these effects started with a simple bias, adding a hammer head in line-ends to prevent line-end shortening. This first-generation correction was called rule-based optical proximity correction (OPC). Then, as chip feature sizes continued to shrink, OPC became more complicated and evolved to a model-based approach. Some extra patterns were added to masks, to improve the wafer process window, a measure of resilience to manufacturing variation. Around this time, the concept of inverse lithography technology (ILT), a mathematically rigorous inverse approach that determines the mask shapes that will produce the desired on-wafer results, was introduced. ILT has been explored and developed over the last three decades as the next generation of OPC, promising a solution to several challenges of advanced-node lithography, whether optical or extreme ultraviolet (EUV). Today, both OPC and ILT are part of an arsenal of lithography technologies called resolution enhancement technologies. Since OPC and ILT both involve computation, they are also considered as part of computational lithography. We explore the background and history of ILT and detail the significant milestones that have taken full-chip ILT from an academic concept to a practical production reality.

The hammerhead self-cleaving motif as a precursor to complex endonucleolytic ribozymes.

Connections between distinct catalytic RNA motifs through networks of mutations that retain catalytic function (neutral networks) were likely central to the evolution of biocatalysis. Despite suggestions that functional RNAs collectively form an interconnected web of neutral networks, little evidence has emerged to demonstrate the existence of such intersecting networks in naturally occurring RNAs. Here we show that neutral networks of two naturally occurring, seemingly unrelated endonucleolytic ribozymes, the hammerhead (HH) and hairpin (HP), intersect. Sequences at the intersection of these networks exhibit catalytic functions corresponding to both ribozymes by potentially populating both catalytic folds and enable a smooth crossover between the two. Small and structurally simple endonucleolytic motifs like the HH ribozyme could, through mutational walks along their neutral networks, encounter novel catalytic phenotypes, and structurally flexible, bifunctional sequences at the intersection of these networks could have acted as nodes for evolutionary diversification in an RNA world. Considering the simplicity and small size of the HH ribozyme, we propose that this self-cleaving motif could have been a precursor to other more complex endonucleolytic ribozymes. More generally, our results suggest that RNAs that possess distinct sequences, structures, and catalytic functions, can potentially share evolutionary history through mutational connections in sequence space.

Research on the Structure and Performance of Bimetal Composite Hammer

In order to improve the service life of the hammer head of the crusher, the high chromium cast iron-medium carbon low alloy steel double liquid composite hammer head is used to replace the single material high manganese steel hammer head; the production process uses lost foam casting instead of sand casting. This article mainly studies the production technology of composite hammers from the aspects of hammer material selection, model making, pouring system design, pouring process and heat treatment process, and uses a metallurgical microscope to observe the bonding interface, and uses a scanning electron microscope to observe both sides of the interface. For element diffusion, the universal testing machine tests the interface combination. The results show that the composite hammer has a firm bonding surface and good bonding quality.

Study on cushioning and energy absorption of sports mouthguard

PURPOSE Using impact test to study cushioning and energy absorption of sports mouthguard of different thickness, material and combination. METHODS According to the thickness, material and combination, the mouthguards were divided into 7 groups with 6 testing pieces in each group. A pendulum device was used to apply impact energy to the mouthguard and dentition model, and the magnitude of the impact energy was measured by changing the release height of the pendulum. The force sensor and the laser vibrometer were respectively connected to the data acquisition and signal analyzer to obtain the incident speed, rebound speed, maximum collision force, collision start time and collision end time of the hammer head. Collision time, energy absorption and energy absorption ratio of the mouthguard were calculated, which reflected different mouthguard cushioning and energy absorption characteristics. One-way analysis of variance and t test in SPSS 22.0 software package was used to analyze the difference between different groups. RESULTS No matter what type of mouthguard was worn by the dentition model, the impact force was significantly reduced than without mouthguards. At the same height, there was significant difference between the average maximum collision force and the average collision time among soft mouthguards with thicknesses of 2, 3, 4, and 5 mm(P<0.05); among which the average maximum collision force of the 5 mm was the smallest and the average collision time was the shortest. There was no significant difference in the average energy absorption and the average energy absorption ratio among these 4 groups. There was significant difference in the average maximum collision force, average collision time, average energy absorption and average energy absorption ratio between the two groups of mouthguards with the same thickness of splints and different materials(P<0.05). Among them, the average maximum impact force of the 4 mm soft mouthguard was smaller and the average collision time was longer. CONCLUSIONS Wearing sports mouthguard can reduce the risk of tooth fracture during collision. Soft mouthguard has the best cushioning performance and it is positively related to thickness. Locally strengthening hard materials can enhance energy absorption and provide better protection.

Kinematic analysis of hammer head acceleration motion during the turn phase in hammer throwers with different record levels

Kinematic analysis of hammer head acceleration motion during the turn phase in hammer throwers with different record levels

Algorithm of Energy-Saving Control Over Hammers of Active Excavator Buckets

The article considers the operation of excavators designed to mine hard or frozen soils. To reduce significant energy consumption, which characterizes the process, active buckets equipped with special hammers are used. Minimizing the energy consumption of such buckets can be achieved by optimally controlling their operating modes. Expressions for the energy consumed by a hammer, characteristics of its head, operating modes, soil are derived, with the minimum of the energy estimated. On the basis of those expressions, an algorithm of energy-saving control over hammers of active excavator buckets is formed and described. It determines the corresponding speed of impact of the hammer head on the soil which can be supplied to the hammer control system in the form of a command signal. The combination of all speeds when digging a track will provide the required performance of the excavator, with each speed set to the minimum, from the viewpoint of optimizing the energy consumption, necessary for the work of the hammer.

Numerical analysis of RC hammer head pier cap beamsextended and reinforced with CFRP plates

This paper presents a numerical study on structural behavior of hammer head pier cap beams, extended on verges and reinforced with carbon fiber reinforced polymer (CFRP) plates. A 3-D finite element (FE) model along with a simplified analytical model are presented. Concrete damage plasticity (CDP) was adapted in the FE model and an analytical approach predicting the CFRP anchor strength was adapted in both FE and analytical model. Total five quarter-scaled pier cap beams with various CFRP reinforcing schemes were experimentally tested and analyzed with numerical approaches. Comparison between experimental results, FE results, analytical results and current ACI guideline predictions was presented. The FE results showed good agreement with experimental results in terms of failure mode, ultimate capacity, load-displacement response and strain distribution. In addition, the proposed strut-and-tie based analytical model provides the most accurate prediction of ultimate strength of extended cap beams among the three numerical approaches.

Simple and Affordable Kinetic Assay of Nucleic Acids by Gel Staining

In an effort to circumvent the pitfalls of using radioactive labeling to measure kinetics in undergraduate labs, a gel staining kinetics assay was developed. The IR‐3 enzyme and substrate, a single stranded DNA that cleaves another single stranded DNA only in the presence of Zn++, was used as a simple and inexpensive DNA model. The rate of the IR‐3, or D‐Zyme, was successfully determined by staining PAGE‐Urea gels with SYBR Gold and then viewing them at 302 nm with epi‐illumination. The open source software ImageJ (version 1.52K) was utilized to quantify the relative band intensities, the ratio of cleaved product to the addition of product and substrate, gave percent cleavage. When percent cleavage was plotted against time in Minitab (version 18.1, Minitab, Inc.), the rate of the reaction could then be determined by nonlinear regression curve‐fitting to the single exponential. To certify this technique, it was also tested on two other models, one being a modified version of the D‐Zyme, while the other was a known Hammer Head Ribozyme, trans RzB. It was demonstrated that the use of SYBR Gold post‐migration staining can be used to quantify RNA and DNA bands for cleavage kinetic analysis, without substrate labeling. Although this method is comparatively less sensitive than radioactive and fluorescence labeling, it has several advantages such as: i) ease of use; ii) cost effective; iii) no half‐life decay; iv) absence of substrate labeling; v) precision enabling curve‐fitting; vi) versatility with non‐structured and structured RNAs or DNAs.Support or Funding InformationMonmouth University Summer Research Program

Effects of Robotic Hammer Peening on Structural Properties of Ni-Based Single-Crystal Superalloy: Dislocation Slip Traces and Crystallographic Reorientations

We studied the morphological and crystallographic properties of Ni-based single-crystal superalloys, addressing their surface and near-surface structural evolutions upon robotic hammer peening (RHP) by employing surface profiling, X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction. By varying the diameter (DHH) of the spherical hammer head and the driving pressure (PRHP), we found that the RHP process with the increased DHH and PRHP tends to improve the surface smoothness and, meanwhile, reduce the RHP-induced step height at the boundary between the peened and unpeened areas, especially on the surface with a deformed layer caused by wire electrical discharge machining (EDM). The surface step height can also be reduced by removing the EDM-deformed layer before the RHP process. Straight and crosshatching DSTs were observed in the transition zones surrounding the peened area, where none or minor crystal reorientations occurred. In comparison, the RHP-induced crystal reorientation is much more significant in the peened area and the reorientation direction is associated with the surface normal direction, i.e., the compression loading axis of the RHP process. The RHP-induced crystal reorientations are discussed and attributed to the non-Schmid behavior associated with multiple cross-slips of superalloys under dynamic compressive loadings.

Cyclic load behavior of precast self-centering hammer head bridge piers

ABSTRACT Five-hammer head bridge piers were fabricated and tested under cyclic lateral loading to evaluate the hysteretic response and the self-centering capability. The failure modes, hysteretic load-displacement loops, dissipated energy, and residual displacement were observed and analyzed. In addition, the seismic performance of proposed construction method with and without energy dissipation rebar, different level of posttensioning were studied. The test results were used to verify the Finite Element Model (FEM) developed in this study. Tested specimens were modeled using the ABAQUS platform under quasi-static loading. The analytical model considered interaction between precast elements, unbonded strands, and surrounding concrete and bond slip between column main reinforcement and concrete. Developed FEM for monolithic bridge pier showed comparable results with the experimental tests. FEM was able to predict the hysteretic behavior of modeled bridge piers with high degree of accuracy. In addition, FEM confirmed the experimental observations and showed that precast self-centering hammer head bridge piers system is capable of withstanding any large lateral displacements before achieving the peak lateral strength. Sensitivity analyses was conducted to investigate the effect of mesh size and bond-slip interaction. Finally a parametric study was conducted to study the effect of construction method, energy dissipation rebar ratio and socket depth on the hysteretic response of the modeled bridge piers. This study reveals that FE analysis using the proposed model is validated to be used in determining the appropriate range of applied posttensioning force; energy dissipation rebar ratio and recess depth.

Biomechanical study of hammer head speed and handle motion at different record levels in the hammer throw

Biomechanical study of hammer head speed and handle motion at different record levels in the hammer throw

Stepwise approach in the management of penile strangulation and penile preservation: 15-year experience in a tertiary care hospital

ABSTRACTObjective: To present our stepwise approach to the management of penile strangulation and penile preservation with 15 years’ experience in a tertiary care hospital, as penile strangulation is a rare urological emergency that requires immediate attention.Patients and methods: A prospective observational study was performed from March 2003 to December 2018 of patients presenting with penile strangulation to our hospital.Results: Nine patients with penile strangulation presented to us between March 2003 and December 2018. The most common motive for the application of a foreign body was sexual gratification (four patients). Three of the nine patients had a mental disorder. Objects used for strangulation included: metallic nut (three), metallic ring (two), plastic bottle (two), wooden hole (one), hammer head (one), and horse hair to control bleeding during circumcision (one). Most of the foreign bodies were located in the proximal penile region. The mean operative time was 38 min and three of the nine patients had complications.Conclusions: Penile strangulation is one of the rare urological emergencies experienced by a urologist. Removal of the foreign body can be difficult and there is no universal method of removal, as each case differs. So, following our stepwise approach can aid in removal of foreign body quickly and preserve the penis from fatal outcomes. Urologist should be aware of all the available armamentarium used for the removal of such foreign bodies.Abbreviation: SPC: suprapubic cystostomy

Practical investigation into piercing process using forging hammer head with filling

Abstract The paper presents the experimental results of the investigations into the impact deformation during the piercing of a lead workpiece using a forging hammer. The results show an increase into the impact efficiency and reduction into the number of required impacts when using hammer head filled with steel beads.

Plant Gene Knockout and Knockdown by CRISPR-Cpf1 (Cas12a) Systems.

CRISPR-Cpf1 (Cas12a) is a class II type V endonuclease, which has been used as a genome editing tool in different biological systems. Here we describe a fast, efficient, and user-friendly system for CRISPR-Cpf1 expression vector assembly. In this system, the Pol II promoter is used to drive the expression of both Cpf1 and its crRNA, with the crRNA flanked by hammerhead (HH) and hepatitis delta virus (HDV) ribozyme RNAs for precise crRNA processing. All the components of this system can be modified depending on plant species and experimental goals. Using this system, nearly 100% editing efficiency and 90% gene expression decrease were achieved in rice and Arabidopsis, respectively.

Biomechanical study of handle movement that gains hammer head speed in turn phase.

Biomechanical study of handle movement that gains hammer head speed in turn phase.

Research on Pneumatic Hammer Used in the Experiment of Forging Process Course

In order to provide simple and practical experimental equipment for the experiment of forging technology course, based on the impact cylinder, the pneumatic hammer used in experiment of forging process course was developed. According to upsetting deformation energy of the lead specimen and the biggest impact energy of impact cylinder, inner diameter and piston stroke of cylinder were chosen. According to the working principle of impact cylinder, the control circuit of the impact cylinder was designed, the electrical components and control components were selected and used, the support bracket of impact cylinder and the anvil block were designed and manufactured. When air pressure is 0.7 MPa, the switch is pressed, after delay the hammer head moves downward at a high speed. The pneumatic hammer has simple structure, small footprint, low noise and vibration. Its impact energy can meet the need of upsetting deformation of lead specimen with a diameter of 20mm at room temperature.

Development of wear resistant hammer heads for coal crushing application through experimental studies and field trials

Coke is one of the most important raw materials for iron making through blast furnace route. Strength and reactivity of coke plays a huge role in efficiency of the counter-current reactor. In order to attain the desired quality of coke, large lumps of coals are crushed in to smaller size fraction in a crushing mill using rotating hammers. However, the heads of these hammers fail prematurely during service that requires their frequent replacements along with interruption in production. This paper presents failure analysis of a coal crushing hammer head with its detailed metallurgical characterization. Analysis revealed that hammer heads fail in abrasive wear mode due to lean chemistry of the alloy used and lower hardness that manifests as higher abrasion rate. 6Cr1Mo steels were supplied in quenched and tempered conditions to a hardness of around 52 HRC. There was presence of only iron chromium carbides that is not sufficient to withstand an application involving extreme wear.The second part of this paper presents detailed chemistry-microstructure-wear resistance correlation for four different alloys; 6Cr1Mo, 20Cr1Mo, complex refractory alloy carbides and tungsten carbide weld deposited hard-facing. Microstructural analysis and phase identification is carried out using scanning electron microscope coupled with electron probe micro-analyzer, x-ray diffraction and Vickers hardness tester. Dry sand abrasion tests were carried out for the existing 6Cr-1 Mo steel and proposed trial specimens. Study shows that the abrasion resistance is strongly a function of type of carbides and their volume fraction. Niobium carbide and tungsten carbides are much more effective in improving the abrasion resistance of alloys compared to primary chromium carbides. Tungsten carbide hard-facing demonstrated the best abrasion resistance. Based on the study, a new design for hammer head with tungsten carbide hard-facing is developed and field trial revealed an improvement in service life greater than three times compared to existing 6Cr1Mo quenched and tempered hammer heads.

Improving the preparation of the liner for rolling on the pilger mill

Purpose. Based on the analysis of the features of the hot piligrim pipe rolling process, develop a new and improved method for preparing liners on the mandrel by compressing their hind ends with specialized strikers of a horizontal hydraulic press. Metodology. The solution to the problem of determining the average specific application on the contact of the liner with the mandrel during compression of its rear end by specialized press dies using the method of slip lines. Findings. The article presents the results of a theoretical determination of the average specific pressure and the width of the contact surface area between the sleeve and the mandrel when the rear end of the sleeve is compressed by specialized strikers of a horizontal hydraulic press. The results obtained allow us to determine the conditions for preventing the liner from slipping from the mandrel as they move toward the rollers in the braking phase. Originality. The main factors affecting the adhesion of the liner to the mandrel were determined, and the values of average specific pressures on the contact of the metal with the mandrel were calculated during the reduction by the profile dies, as well as the width of the contact area and the required thickness of the dies. It has been established that the thickness of the strikers of a double-sided press can be assumed to be the same for all sizes of sleeves of the assortment TPA 5-12 ''. Practical value. The results of the theoretical studies can be used to modernize and reconstruct a section of the off-site charging of a pilger mill TPA 5-12 '' by installing horizontal hydraulic presses with double-die profile dies. This will increase the productivity of the mill by preventing the sleeve from sliding down the mandrel during roll-up to the rolls by creating the necessary adhesion forces between the sleeve and the mandrel. In addition, it will facilitate the conditions of the seed regime piligrim rolling, which will reduce machine time and increase productivity. Key words: pipe, liner, pilgrim mill, hydraulic press, hammer head, mandrel, performance.

Analysis of spindle bearing load with regard to the false brinelling effect caused by machine hammer peening

Machine hammer peening (MHP) is a high-frequency incremental forming process for surface treatment, which is used on milling machines. Because of the stationary motor spindle as a result of the pneumatic and electrical connections to the hammer head, point loads can occur and may initiate false brinelling wear on the spindle bearing rings. The aim of this work is an experimental and numerical analysis of the interdependencies between MHP reaction forces on the spindle adapter and bearings as well as the associated false brinelling wear of the spindle bearing rings during MHP. Firstly, MHP reaction force measurements on a servo-mechanical press with high stiffness with variation of frequency, electrical power, and time were conducted. Secondly, the spindle bearing wear during MHP was analyzed using fatigue tests and complementary simulations by means of numerical FE-software Abaqus 6.14 and software NewSpilad and WinLager. Thirdly, the effect of damaged spindle bearings on the milling operation was analyzed by means of an endurance test system for bearings. The results showed that false brinelling wear on spindle bearing rings occurs at frequencies around fmhp = 100 Hz and maximum reaction forces of Fcompr. = 3,450 N during MHP on milling machines. Furthermore, a significant raise in temperature of the damaged spindle bearing from Tinitial = 25 °C to Tfinal > 80 °C during fatigue test using 5.76 × 106 load cycles could be detected. Thus, a damaged spindle bearing is not suitable for application in permanent operation. However, at frequencies around fmhp = 200 Hz, no false brinelling wear could be detected and the temperature did not raise significantly during fatigue test. Therefore, this undamaged spindle bearing can be used without impairment for permanent operation.